1. Field of the Invention
The present invention relates to a technology of multiplexing service traffics of a plurality of layers 1 to 3 on the same carrier wave in a transmission network including a lightwave network.
2. Description of the Related Art
As multimedia communication services such as a transmission of voices and images and a connection to the Internet have been widespread, the demand for a large capacity communication path has increased. A physical infrastructure has been well equipped, and various services suitable for the respective networks have been provided. A transmission system from a service receiver (hereinafter referred to as a “client”) has been varied into protocols such as an asynchronous transfer mode (ATM), a frame relay, a point-to-point protocol and a giga-bit ether. Since these protocols do not have compatibilities, they cannot be multiplexed as they are.
As a method of performing a transmission of these protocols by the one and only carrier wave, a method of converting the protocols into one protocol among the protocols to form a common frame and of unifying and processing the entire traffics is conceived.
(Please refer to Japanese Patent Laid-Open No. Hei 8-321833, Japanese Patent Gazette No. 2768297, Japanese Patent Laid-Open Nos. Hei 10-135986, 9-93305 and 9-36875.) FIG. 8 to FIG. 10 show the cases where ATM is used as a common frame and a frame relay is used as the common frame.
FIG. 8 shows the conventional processing system used when a client data frame 110 is transferred as an ATM cell 130 by use of an A™ adaptation layer type 5 (AAL5). This system is standardized according to “Multiprotocol Encapsulation over ATM Adaptation Layer 5” of IETF RFC 1483 (Juha Heinanen, Telecom Finland, July 1993).
An AAL5 frame 120 is constituted by adding the following bytes at the rear of the client data frame 110. Specifically, eight bytes of a new overhead which includes a CPCS-PDU Length information area 122 (two bytes) indicating a size of the client data frame 110 and a CRC information area 121 (four bytes) for error check are added, and a padding area 125 which adds zero to forty seven bytes so that the size (bytes) of the AAL5 frame 120 can be a multiple of forty eight bytes is added.
With the AAL5, the AAL5 frame 120 is split into each forty eight bytes 131, and five bytes of a common overhead 132 is added to each forty eight bytes 131, thus a plurality of ATM cells 130 are generated. In this case, only a final ATM cell 130-n is clarified as a final cell of the AAL5 frame 120 by turning a bit located at a lowest position of a PTI field in an overhead 132-n into one. Then, the ATM cells 130 are mapped into payload portions of the respective media.
FIG. 9 shows a state, as an example, where one of the ATM cells is mapped into a SONET payload portion. A SONET is constituted of a SONET overhead (SOH) 210 and a SONET payload 220, and the ATM cell 130 is mapped into the SONET payload 220 in such forms shown in signal blocks 221.
A node shown in FIG. 9, which has received a carrier wave such as the SONET refers to the overhead 132 after extracting the ATM cell 130. If the ATM cell 130 is an ATM connection to be terminated, the ATM cell 130 is managed for every ATM connection. In the node, when the ATM cell 130-n having the lowest position bit value of one is received, the overhead 132 is deleted from the ATM cell 130, and the rest thereof is converted into the AAL5 frame 120. Thereafter, the client data frame 110 is reconstructed.
In such a manner, various client data frames can be multiplexed on the same carrier wave by use of the ATM, and a desired client data frame transfer can be realized between clients transmissively.
FIG. 10 shows the conventional processing example where a frame relay 300 is used as a common frame. The frame relay 300 imparts two bytes of an address information area 302 to the head of the client data frame 110, and imparts four bytes of an error check information area 303 at the rear of the client data frame 110. Thus, data is constituted.
To the head and the rear of the data thus constituted, flags 301 and 304, each of which has one byte of the information area, are imparted to encapsulated, thus the frame relay 300 is constituted. The frame relay 300 thus constituted is mapped as the signal blocks 221 into the payload 220 similarly to the ATM cell 130 as shown in FIG. 9. The node having received a row of such signals as shown in FIG. 9 extracts the frame relay 300 by detecting the flags 301 and 304.
Thereafter, the address information area 302 is referred. And hence, if the frame relay 300 is the one to be terminated, the flags 301 and 304, which serve as the overheads of the frame relay 300, the address information area 302, the error check information area 303, are deleted to return the frame relay 300 into the client data frame 110. When the frame relay 300 is constituted, byte insertion is performed so that patterns of the flags 301 and 304 cannot exist within the frame relay 300.
As described above, various client data frames can be multiplexed on the same carrier wave by use of the frame relay, and a desired client data frame transfer can be realized between clients transmissively.
In the case where the ATM cell is used as a common frame as described above, since the overhead having fifty-six bytes at maximum is added for constructing the AAL5 frame, an amount of the overhead is increased. Moreover, in the case of the ATM cell, since it is necessary to split the AAL5 frame into forty eight bytes of the ATM cells, which are small, and to add overheads thereto, there has existed a problem that 10% or more of a band is used.
Moreover, in the case where the AAL5 frame is reconstructed by a receiver, a group of cells of the same connection must be split to be managed. Accordingly, in the case where the receiver has to deal with many connections, there is a fear that an operation speed may be limited.
Furthermore, in the case where the frame relay is used as the common frame, since the byte insertion must be performed so as not to cause the same pattern as those of the flags in the frame, there is a fear that a transfer frame length may be extended almost twice in some cases, leading to a low efficiency.
Still further, in the case where the frame relay is used as the common frame, the ATM cell is also encapsulated. This results in a further addition of a overheads to the ATM cell, leading to a significantly lower efficiency.
The object of the present invention is to provide a technology of multiplexing data traffics of layers 3 or more including an IP packet and a plurality of layer 2 frames such as an ATM, a PPP, an Ether and an STM on a same carrier wave efficiently.